Engine knock, which can create uncontrolled combustion in vehicle internal combustion engines, is a condition that typically occurs when ignition timing of the vehicle engine is advanced improperly. To avoid engine knock, which can lead to engine damage, engine knock sensors are often used. Engine knock sensors are typically configured to detect which cylinder or cylinders of an internal combustion engine are experiencing a knock condition. When engine knock sensors are coupled to vehicle engine control modules that control the operation of the engine, the vehicle engine control module can monitor the engine knock sensors, and modify the ignition timing of the engine until the knock condition is no longer detected by the engine knock sensors. Engine knock sensors can also be employed to help vehicle engine control modules to determine how to adjust the timing of the engine to provide improved fuel economy and torque.
To detect engine knock conditions, engine knock sensors typically require the use of appropriate sensor interface circuitry and adequate filtering in order for a system employing an engine knock sensor to correctly detect knock signals issued by the engine knock sensors. Typical engine knock sensor interfaces sense the knock signals provided by engine knock sensors differentially, and then use a first or second order low-pass filter to filter the knock signal. The filtered signal is then typically provided to an analog-to-digital converter for conversion into digital form, so that the digitized knock signal can be analyzed by digital processing circuitry to determine if an engine knock condition is occurring. The nature of the filter required to optimally filter the knock signal typically depends, in part, on the speed of the analog-to-digital converter to which the filtered signal is provided. Higher order filters having higher filter Q factors are typically desired for systems employing slower analog-to-digital converters. However, filters having a higher order and a higher filter Q factor are typically not necessary for systems employing fast analog-to-digital converters. Some interface integrated circuit manufacturers integrate a second order filter structure on the interface integrated circuit, so that the interface integrated circuit can be more easily used with slower analog-to-digital converters. While this may prove beneficial for systems employing a slow analog-to-digital converter, additional die area is typically required for the second order filter structure, and additional cost in terms of system architecture may also be required to support the second order filter structure. These added costs can make the use of an integrated circuit having integrated second order filter structure less than optimal for systems employing a fast analog-to-digital converter, and therefore, not typically requiring a second order filter structure. In addition, by providing an integrated second order filter having a higher Q, the gain of the output signal is increased above the level it would have if a first order filter with a lower Q were employed. This additional gain in the output signal typically leads to loss of signal dynamic range.
What is needed is interface circuitry having gain and Q characteristics that can be easily modified through the use of components external to an interface integrated circuit, and through electronic signals provided to the interface integrated circuit, such that a single integrated circuit can be reconfigured to be used to support multiple platforms having analog-to-digital converters of various speeds.